Many wireless smart devices such as smart phones and tablets are equipped with multiple interfaces to allow access to wireless networks based on cellular technologies such as LTE and to other wireless networks based on Wi-Fi technology, as shown in FIG. 1.
FIG. 1 is a logical diagram showing a cellular base station (BS) 102 and a Wi-Fi access point (AP) 104 as two separate physical entities. In practice these two network entities can be co-located. Cellular networks operate in licensed bands where operation is limited to a single operator network and no sharing with other devices is allowed. Operation in licensed bands enables cellular networks to support elaborate resource sharing mechanisms and precise synchronization. Resource allocation and synchronization information usually are transmitted from the BS 102 to user equipments (UEs) 106 using dedicated control channels.
On the other hand Wi-Fi networks operate in unlicensed bands where interference from other (non-Wi-Fi) devices is common. Consequently, transmission opportunities (TXOPs) for stations (STAs) 108 are allocated on a random basis using carrier sense multiple access with collision avoidance (CSMA/CA). Uplink (UL) and downlink (DL) transmission periods are not scheduled. This is in contrast to cellular networks, where UL and DL are scheduled and the schedule is kept at all participating network devices.